Electrolytic process of making diacetone 2-keto gulonic acid



United States Patent 3,453,191 ELECTROLYTIC PROCESS OF MAKING DI- ACETONE 2-KETO GULONIC ACID Gerhard Joseph Frohlich, Ridgewood, Allan Jerome Kratavil, Wayne, and Edward Zrike, Belleville,

N..I., assignors to Hotfmann-La Roche Inc., Nutley,

N.J., a corporation of New Jersey No Drawing. Continuation-impart of application Ser. No. 574,914, Aug. 24, 1966. This application July 21, 1967, Ser. No. 654,992

Int. Cl. 'C07b 3/00; Blilk 1/00 U.S. Cl. 204-78 17 Claims ABSTRACT OF THE DISCLOSURE Diacetone sorbose is electrolytically oxidized to diacetone-2-keto gulonic acid in an aqueous alkaline medium utilizing as the anode an activated nickel oxide, i.e., a nickel oxide in which the average valence of the nickel is between about 2.7 and 4. Yields of about 90% are obtained.

RELATED APPLICATIONS This application is a continuation-in-part of copending U.S. patent application Ser. No. 574,914, filed Aug. 24, 1966 by Frohlich et al. and entitled, Electrolytic Process.

BACKGROUND OF THE INVENTION Heretofore the oxidation of diacetone sorbose to diacetone 2-keto gulonic acid has been effected by a bleach, e.g., sodium hydochlorite in the presence of an oxygen carrier in solution. There have also been some efforts to employ electrolytic means for the same conversion. Among the latter are efforts to oxidize diacetone sorbose electrolytically in the absence of any oxygen carrier or in the presence of oxygen carriers, e.g., soluble per-salts, bichromates and permanganates. Other efforts at electrolytic oxidation of diacetone sorbose include the use of oxidation catalysts, e.g., inorganic nitrites or nitrates, particularly ammonium, sodium or potassium nitrites or nitrates. Further attempts to improve the electrolytic oxidation of diacetone sorbose to diacetone 2-keto gulonic acid involve the use of the combined action of a halide and soluble chromium compounds. All of the foregoing methods have been found inadequate from a commercial standpoint in that the processes have proven to be too expensive and the yields insufficient to permit large-scale production on a competitive basis.

SUMMARY OF THE INVENTION This application relates to the conversion of diacetone sorbose to diacetone 2-keto gulonic acid. More particularly, the invention described hereinafter pertains to the oxidation of diacetone sorbose to diacetone 2-keto gulonic acid by electrolytic means.

It has been found that when diacetone sorbose is added to an aqueous alkaline medium in an electrolytic cell having an electrode on which is deposited an activated nickel oxide, i.e., a nickel oxide bearing a labile oxygen and in which the average valence of the nickel is between about 2.7 and 4 and an electric current is then passed through said cell, diacetone sorbose is oxidized to diacetone 2- keto gulonic acid. Indeed that oxidation results in very substantial yields of diacetone 2-keto gulonic acid, i.e., yields approximating 90% or greater.

DETAILED DESCRIPTION OF THE INVENTION In accordance with the present invention, diacetone sorbose is placed in an electrolytic cell, e.g., an electrolysis 3,453,191 Patented July 1, 1969 tan-k which may or may not be provided with a cell divider or membrane, and which is provided with an anode and a cathode. The cathode can be made of most any material commonly employed for making cathodes in the electrochemistry art, e.g., Monel, stainless steel, platinum or palladium, etc. The anode can be any material which is conductive, is conventionally used as an anode and to which an activated nickel oxide will adhere, e.g., Monel, stainless steel, sintered nickel, graphite, carbon and the like. It is significant to recognize that the present invention utilizes the activated nickel oxide coating itself as the anodic electrode. Thus, the conventional anodes referred to above are employed in this invention solely as a conductive support for said activated nickel oxide electrode. It is not essential to the invention that the nickel oxide be supported, however, it is preferred. The activated nickel oxide coating employed as the electrode in the process of this invention is not to be confused with metallic nickel alloys previously employed as anodes in the electrochemistry art. For example, Monel which is a nickel alloy, nickel being the dominant constituent, would be a totally unsatisfactory anode in the instant process. Indeed if a nickel alloy, e.g., Monel, is employed in the process of this invention in the absence of a nickel salt in the electrolyte, little or no oxidation of diacetone sorbose will occur. Thus, it is a unique aspect of the instant process that the activated oxide coating serves as the electrode.

In the preferred embodiments of this invention, the conductive anodic support can be first coated with an activated nickel oxide and then employed in the process described hereinafter, or the conductive anodic support can be coated as a first step in the process. That is, the presence of a nickel, salt, e.g., nickel nitrate, nickel sulfate, nickel acetate, nickel formate and the like, in the electrolytic medium during electrolysis will result in the deposition of nickel oxide on the conductive anodic support and the coating of nickel oxide will then act as the electrode. The nickel oxide electrode can also be formed by impregnating a sintered nickel plate with nickel salts until the surface and pores of the plate are coated with nickel salt. The nickel salt will be converted to the nickel oxide in the presence of an anodic current. In addition, nickel-plated cast iron could be used as the electrode support.

The activated nickel oxide employed as an electrode in the instant process must, at the moment of reaction, be of a higher valence nickel oxide, i.e., the nickel ion must be of a valence greater than 2. During the electrolysis an erosion of the activated nickel oxide from the surface of the anode support may occur. Hence, to stabilize the activity of the activated nickel oxide electrode during the process, it is desirable to introduce a small quantity of a nickel salt to the electrolytic media with each introduc tion of reactant. However, it is not critical to the operability of the process of this invention that a nickel salt be introduced into the electrolytic media, however, in order to utilize the preferred process of this invention, the addition of the salt is desirable. As already indicated, the added nickel salt will decompose during electrolysis and deposit as a coating of activated nickel oxide on the surface of the conductive anodic support. Nickel hydroxide which can be formed upon the introduction of a nickel salt to the alkaline electrolyte or added as such becomes suspended in the electrolytic solution thereby creating a heterogeneous nickel oxide-hydroxide solution. The nickel hydroxide suspended in that solution will deposit on the anodic support on the passing of a current through the heterogeneous nickel oxide-hydroxide solution.

The nickel salt employed to produce the activated nickel oxide electrode is a salt of nickel which when added to an alkaline medium forms nickel hydroxide, e.g., the nitrate, sulfate, acetate, formate and the like. The numerical averages of the valences of the nickel of the nickel oxide electrode must fall between approximately 2.7 and 4 in order for the oxide to be active and thus useful in this process. The presence of any amount of activated nickel oxide in the electrolyte solution can effect the reaction. However, the amount of nickel oxide present should be at least sufiicient to cover the conductive electrode support surface. It is desirable, however, that an excess of nickel oxide be present, suspended in the electrolyte. That is, during the process it is desirable that the amount of activated nickel oxide which is present suspended in the electrolytic solution be formed from about 0.001 mole to about 0.5 mole of nickel salt per mole of diacetone sorbose, with about 0.05 mole of nickel salt per mole of diacetone sorbose being preferred.

To the electrolytic cell containing diacetone sorbose is then added an aqueous alkaline solution, e.g., sodium or potassium hydroxide, preferably sodium hydroxide, in water as the electrolyte. It is most important that the total alkali used be added gradually or intermittently to the reaction solution to avoid precipitation of the diacetone sorbose. It is desirable that the aqueous alkaline solution be employed in excess stoichiometric proportion to the molar quantity of diacetone sorbose. Optimum yields are obtained when applying from about 1.9 to about 2.1 moles of alkaline material, e.g., sodium hydroxide, per mole of diacetone sorbose although any proportion in excess of 1 mole of alkaline material per mole of diacetone sorbose can be employed. The pH of the solution should be maintained at greater than 9, optimally at from about 12 to about 13. The reaction can be conducted at a temperature at from about 25 C. to about 85 C., optimally from about 55 C. to about 75 C.

In practice it is desirable to introduce the diacetone sorbose into the electrolytic cell in the form of a solution containing diacetone sorbose, alkaline media, e.g., sodium hydroxide, nickel salt and water.

The electrolytic cell can be provided with a stirrer or mechanical agitator, or the solution can be circulated by means of pumps. The electric current passed through the solution can be of a current density of up to about 15 amperes per square decimeter with about 0.5 amperes per square decimeter to about 6 amperes per square decimeter being preferred. The molar quantity of diacetone sorbose in the electrolyte determines the required current, e.g., 4 faradays are required to oxidize 1 mole of diacetone sorbose assuming 100% current efficiency.

On termination of electrolysis, the diacetone 2-keto gulonic acid is separated from the electrolyte by methods well known to the art. It has been found that in the aforedescribed process, the reaction is irreversible and no hydrogen de-polarizer is necessary to prevent the reversal.

The following examples are illustrative of the aforedescribed invention but not limitative thereof.

Example 1 A 1000 ml. resin reaction flask provided with a mechanical stirrer and a condenser was placed in a constant temperature water bath to maintain reaction temperature. In the flask at 32 square inch 30 mesh stainless steel cylindrical anode was inserted and a spiral nickel wire to act as the cathode was also inserted.

The reaction solution charged to the flask consisted of 300 ml. technical diacetone sorbose solution (123 grams diacetone sorbose), 600 ml. of water, 32 ml. 50% NaOH and ml. 9.6% Ni(NO The temperature was adjusted to 55 C. with agitation and 4 amperes of current was applied. The current density based on total screen surface area was approximately 0.7 amperes/sq. dec. After /2 hours, 15 ml. of 50% NaOH in 15 ml. H O was added and the passage of current continued until a total of 22 hours (7 F/ gram moles diacetone sorbose) had elapsed. The reaction solution was filtered through Hyflo (a filter aid) and extracted at room temperature 3 times with 250 ml. benzene. The

benzene extract was evaporated under vacuum and a syrup of 2.8 grams unreacted diacetone sorbose was recovered. The aqueous phase was chilled to a temperature of 5 C. and the pH adjusted to a value of 2 with cold dilute HCl. After filtering, washing with ice cold water and drying at room temperature, a product weighing 123.5 grams of diacetone 2-keto gulonic acid monohydrate was obtained. The conversion of diacetone sorbose to diacetone 2-keto gulonic acid was 89.4% and a net yield with the recovered diacetone sorbose was 91.6%.

Example 2 Three 14 x 14 mesh (0.02 in. wire diameter) stainless steel screen cathodes and two 40 mils thick sintered nickel anodes all of 3 in. x 3 in. size and stacked on insulated 2 in. long bolts equidistant in the sequence, i.e., cathodeanode-cathode-anode-cathode, having a total anode area of 36 square inches (2.32 dm. were installed vertically in a vessel. A vibro-mixer was used to provide agitation and was installed so that the mixer plate was positioned horizontally under the electrode stack. The electrodes were preconditioned in 2.2 w./v. percent (weight/ volume percent) NaOH for 2 /2 days at 0.4 amperes before charging the reaction solution. The reaction charged to the cell comprised a mixture of 1030 ml. solution containing 12.0 w./v. percent diacetone sorbose (123 grams, 0.473 gram moles) and 2.4 w./v. percent NaOH (1.3 gram moles NaOH per gram moles diacetone sorbose). The current density applied was approximately 1.7 amperes/drn. for 22 /2 hours (7.1 F/gram moles diacetone sorbose). The temperature was maintained at approximately 56 C., and a second addition of NaOH was added after about 5 F/ gram moles diacetone sorbose of current passage. The isolated diacetone 2-keto gulonic acid was obtained by customary techniques and a conversion of 81.3% was realized. A follow up experiment was performed in which 0.022 mole of Ni(NO -6H O per mole of diacetone sorbose was initially added to the reaction mixture. The addition of nickel nitrate yielded a diacetone 2-keto gulonic acid conversion of 90.7%. The yield based on diacetone sorbose recovery was 92.7%

Example 3 An electrolytic cell consisting of an anode and cathode plate of nickel-plated cast iron and separated by a synthetic fabric cell divider was assembled. An external vessel was utilized to store the electrolyte which was circulated by a pump into the anolyte and catholyte cell chambers. A reaction charge according to Examples 1 and 2 was utilized at a current density of 1.88 amperes/dm. and a current of 6.8 F/gram moles diacetone sorbose and a reaction time of about 23 hours. The nickel nitrate present in the reaction charge was 0.023 gram moles nickel nitrate per gram moles of diacetone sorbose, and a diacetone Z-keto gulonic acid conversion of 89.0% was obtained with a recovery of 1.5% unreacted diacetone sorbose. The net yield realized was 90.5%.

Example 4 A stainless steel flow cell of a design as described in Example 2 was constructed. A reaction charge according to Examples 1-3 was used. A current density of 4.2 amperes/dm. based on total surface area was utilized and the current input was 7.4 F/ gram moles diacetone sorbose. The amount of nickel nitrate added was 0.022 moles/ moles diacetone sorbose. The reaction time was approximately 6 hours. A conversion of 91.4% diacetone 2-keto gulonic acid was obtained, and 2.6% of unreacted diacetone sorbose was recovered. The net yield was 94.0%.

Example 5 A Monel flow cell consisting of an anode and cathode plate separated by a fabric cell divider was fitted with an auxiliary reservoir and pumps for circulation of the electrolyte through the anode and cathode chambers. A temperature of 55 C. was maintained, and a current density of 1.0 amperes/dm. was utilized for the reaction period of 23 hours. A reaction charge according to Examples l-4 was used except that no nickel nitrate was added to the reaction system. After a current passage of about 7.7 F/ gram moles diacetone sorbose, a 22% conversion to diacetone 2-keto gulonic acid was obtained. A 60.4% recovery of diacetone sorbose was obtained to give a material balance of 82.4%. When the above experiment was repeated with, however, the initial addition of 0.018 moles Ni(NO per mole of diacetone sorbose to the reaction system, a conversion to diacetone 2-keto gulonic acid of 93% was obtained, and a material balance of 96.4% based on diacetone sorbose recovery resulted.

Example '6 An electrolytic cell provided with a stainless steel anode (206 cm?) and a nickel cathode (40 cm?) and a mechanical stirrer was charged with the following solution: 123.0 grams pure diacetone sorbose (0.472 mol.), 22.1 grams NaO-H (0.552 mol.) and 0.8 gram NiSO -7H O. A current of 3.84.2 amps. (current density of 2 amps. per square decimeter) was passed through the cell for a period of hours. The batch temperature was maintained at 60 C. On completion of the reaction a yield of 89.1% diacetone 2-keto gulonic acid was obtained and a material balance after recovery of diacetone sorbose was 91.9%.

The electrolytic oxidation process described above finds its most immediate application in the oxidation of diacetone sorbose to diacetone 2-keto gulonic acid, the latter being an important intermediate in the synthesis of ascorbic acid. However, the electrolytic oxidation process of this invention could be applied generally to the conversion of alcohols to carboxy acids and alkaline media.

We claim:

1. In the process of electrolytically oxidizing diacetone I sorbose to diacetone 2-keto gulonic acid, the improvement consisting of passing an electric current through an aqueous alkaline solution containing diacetone sorbose and a nickel oxide electrode.

2. The process of claim 1 wherein the nickel in the nickel oxide has an average valence of from about 2.7 to about 4.

3. The process of claim 2 wherein the aqueous alkaline solution contains an alkaline hydroxide selected from the group consisting of sodium hydroxide and potassium hydroxide.

4. The process of claim 1 wherein the pH of the aqueous solution is at least about 9.

5. The process of claim 1 wherein nickel oxide with an average valence of from about 2.7 to about 4 is present in the aqueous alkaline solution, being formed from about 0.001 mole to about 0.5 mole of nickel salt per mole of diacetone sorbose.

6. The process of claim 1 wherein the temperature of the reaction medium is from about C. to about -85 C.

7. The process of claim 1 wherein the current density of electricity passed through the aqueous alkaline solution is less than about 15 amperes per square decimeter.

8. A process for electrolytically oxidizing diacetone sorbose to diacetone 2-keto gulonic acid which comprises passing an electric current through an aqueous electrolytic solution containing an alkaline hydroxide, diacetone sorbose and an anodic electrode consisting of a conductive support coated with nickel oxide containing nickel of an average valence of from about 2.7 to about 4 and a cathode.

9. The process of claim 8 wherein the alkaline hydroxide is selected from the group consisting of sodium hydroxide and potassium hydroxide.

10. The process of claim 8 wherein the pH of the aqueous alkaline solution is at least about 9 and the temperature is from about 25 C. to about 85 C.

11. The process of claim 8 wherein the electric current density passed through the electrolyte is less than about 15 amperes per square decimeter.

12. The process of claim 8 wherein the aqueous alkaline solution contains nickel salt.

13. The process of claim 8 wherein the conductive support is coated with nickel oxide in situ by passing an electric current through the aqueous alkaline solution containin g a nickel salt.

14. The process of claim 8 wherein the conductive support comprises a sintered nickel plate and the nickel oxide coating is formed in situ by impregnating said sintered nickel plate with nickel salts until the surface and pores of the plate are coated with nickel salt and converting said salt to nickel oxide by means of an anodic current.

15. The process of claim 8 wherein nickel hydroxide is suspended in the electrolytic solution.

16. A process for making diacetone 2-keto gulonic acid which comprises adding diacetone sorbose to an anolyte solution containing as the essential ingredients, water, an alkali metal hydroxide and a nickel salt; passing an electric current through said anolyte by means of a nickel oxide electrode at a current density of from about 0.5 amp/sq. dm. to about 6 amp/sq. dm. to oxidize said diacetone sorbose; and recovering said diacetone 2-keto gulonic acid from the resulting anolyte solution.

17. The process according to claim 16 wherein the anolyte solution is maintained at a pH of from about 9 to about 13 and the temperature of said solution is maintained at from about 5 5 C. to about C.

References Cited 2,960,452 11/1960 Slager et a1 204-78 JOHN H. MACK, Primary Examiner.

H. M. FLOURNOY, Assistant Examiner.

mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent NO- 3,'453,l91 Dated July 1, 1969 Inventor(s) Frohlich, Kratavil and Zr'ike It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 32 "hydochlor-ite" should be: Hypochlorite Page 1, line l? of 0hr specification.

Column 2, line 33 "nickel, salt, should be:

nickel salt, Page 4, line 3 of our specification.

Column 5, Claim 5 line 51 "wherein nickel oxide with an" should be: "wherein nickel oxide containing nickel with an Page 1}, Claim 5, lines 1 and 2 of our specification.

'smuzo mm X SEALED MAY 1 2 1970 (S Attest:

I HM E. 'SGHUYIIER, Atteatmg Officer comissioner of Patmfi 

